1. Field of Invention
The present invention relates to catalysts for hydrogenating olefins. More particularly, this invention relates to supported catalyst for hydrogenating fluoroolefins.
2. Description of Prior Art
Catalytic hydrogenation of fluoroolefins is frequently used in producing hydrofluorocarbons as useful products and/or intermediates. Various metals, such as Pd, supported on a substrate have long been recognized as highly effective hydrogenation catalysts. These catalysts are particularly effective in gas-phase reactions.
In certain reactions, the effectiveness of these catalysts can be increased by incorporating at least one zero-valent metal onto a supporting substrate. Materials such as alumina, silica, titania, and zirconia, as well as titanium oxide, magnesium oxide, and zirconium oxide are known substrates for certain hydrogenation catalysts. (U.S. Pat. No. 5,089,454). Knunyants et al. (see Izv. Akad. Nauk. SSSR, (1960) 1412-1418) reports a Pd/Al2O3 catalyst used to catalyze the hydrogenation of CF3CF═CF2 (HFP) to CF3CHFCHF2 (236ea), and CF3CF═CHF (1225ye) to CF3CHFCH2F (245eb). However, due to the occurrence of hydrogenolytic cleavage of the carbon-fluorin bond, small amount of HF is generated during reaction, which attacks alumina, silica, titania, and zirconia that are known as the normal carrier of palladium, causing catalyst structure change and catalyst deactivation. Japan Patent JP Patent 3543863 teaches the use of a Pd/carbon catalyst that is resistant to HF attack for the hydrogenation of HFP to 236a. U.S. Pat. No. 5,396,000 teaches the use of a Pd/carbon catalyst for the hydrogenation of 1225ye to 245eb. However, these carbon supported metal catalysts are not regenerable once deactivated. Therefore, there is a need for a new type of catalyst that is not only resistant to HF attack but also regenerable once deactivated for the hydrogenation of fluoroolefins.